The overall aim of this project is to investigate in vitro alterations in vascular endothelial cell biology due to contact with sickle erythrocytes. The central hypothesis is that sickle erythrocyte interactions with vascular endothelium alter endothelial cell function and in so doing contribute to the clinical manifestations of sickle cell anemia, in particular cerebral vascular disease. A secondary hypothesis is that these interactions and the ensuing alterations in endothelial cell function are modulated by the hemodynamic environment. The in vitro cell culture studies to be conducted as part of this proposed project are based on four specific aims. These are (i) to study alterations in endothelial morphology, F-actin localization, and extracellular matrix due to interactions with sickle erythrocytes, (ii) to determine the influence of sickle erythrocyte-endothelial interactions on the growth state of vascular endothelial cell monolayers by the measurement of various indices of proliferation, (iii) to investigate whether or not sickle erythrocyte-endothelial interactions alter the expression of growth factors by endothelial cells, and (iv) to examine the effect of sickle erythrocyte-endothelial interactions on the thrombogenicity of vascular endothelial cells by measuring its influence on PGI2 production. A key aspect of this proposed effort is to study vascular endothelial biology under conditions of flow. Such flow studies are important for two reasons. First, as indicated in the secondary hypothesis stated above, the hemodynamic or flow environment in which sickle erythrocyte-endothelial interactions occur may modulate any related alterations in endothelial cell function. Secondly, endothelial cells in vivo normally reside in a flow environment; thus, static culture studies of endothelial biology may at best represent the simulation of a low shear environment and perhaps be fundamentally artifactual in nature.